Earth-boring bit with improved bearing seal

ABSTRACT

An earth-boring bit has a bit body and at least one bearing shaft depending inwardly and downwardly from the bit body. The bearing shaft has a base where it joins the bit body. At least one cutter is mounted for rotation on the bearing shaft and has radial and axial surfaces that cooperate with the base of the bearing shaft to define a bearing seal gland. A bearing is defined between the cutter and bearing shaft. A seal element is disposed in the seal gland. A secondary seal is disposed in the seal gland opposite the cutter axial surface and cooperates with the seal element to at least partially seal the gland against entry of debris from the exterior of the bit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to earth-boring bits,particularly to those having rotatable cutters in which seal assembliesretain lubricant within the bearing areas.

2. Background Information

One of the most successful seal means used in earth-boring bits of thetype having rotatable cutters is the O-ring seal disclosed in commonlyassigned U.S. Pat. No. 3,397,928, to Galle. The o-ring seal successfullyconfines lubricant to the bearing area while excluding detritus for longperiods of time before failure.

A more recent seal development is the rigid or metal face seal. In therigid face seal type, the seal interface is between one or two rigid,usually steel, seal rings. One or two elastomer o-rings serve toenergize or urge the seal faces of the rigid ring or rings in contactwith each other. The rigid face seal has proved to be as successful asthe o-ring seal and provides an improved ability to accommodate pressurefluctuations in the bit lubricant.

A somewhat less successful design is the Belleville seal, in whichelastomer elements are bonded to a rigid metallic ring or washer, whichis placed under compression in the seal gland and the elastomer elementsperform the bulk of the sealing.

All three types of seals are subject to the condition known as mudpacking. This condition occurs when the solid matter in drilling fluidor mud is carried into the seal gland, where it adheres to gland and/orseal component surfaces and causes deformation and/or slippage ofelastomeric seal components. Moreover, these particles can accelerateabrasive wear of all seal components.

A need exists for seal assemblies that supplement the main bearing sealby assisting in the prevention of entry of debris into the seal assemblyitself.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide anearth-boring bit having an improved bearing seal that is more resistantto wear and provides improved sealing efficiency for longer periods intime.

This and other objects of the present invention are achieved byproviding an earth-boring bit having a bit body and at least one bearingshaft depending inwardly and downwardly from the bit body. A bearing isdefined between the cutter and bearing shaft. The bearing shaft has abase where it joins the bit body. At least one cutter is mounted forrotation on the bearing shaft and cooperates with the base of thebearing shaft to form a bearing seal gland. A seal element is disposedin the bearing seal gland. A secondary seal is disposed in the sealgland adjacent the base of the bearing shaft and cooperates with theseal element to at least partially seal the gland against entry ofdebris from the exterior of the bit.

According to the preferred embodiment of the present invention, the sealelement is a rigid face seal, which includes at least one rigid sealring and at least one resilient energizer ring, that seals against entryof debris into the bit bearing.

According to the preferred embodiment of the present invention, thesecondary seal element is a continuous elastomeric ring disposed at thebase of the bearing shaft.

According to the preferred embodiment of the present invention, the bitbody includes a last-machined surface adjacent the base of the bearingshaft. The secondary seal element may be secured by adhesive to thelast-machined surface and/or to the rigid seal ring.

According to the preferred embodiment of the present invention, thesecondary seal element is a resilient ring in contact with a portion ofthe seal element.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal section view of one section of the bit body ofan earth-boring bit according to the present invention.

FIG. 2 is an enlarged, fragmentary longitudinal section view of thebearing shaft and seal according to the present invention.

FIG. 3 is an enlarged, fragmentary section view of the seal assembly ofFIG. 2.

FIG. 4 is an enlarged, cross-sectional view of the secondary, staticseal ring of FIG. 3 in a relaxed condition.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The numeral 11 in FIG. 1 of the drawing designates an earth-boring bithaving a threaded upper portion 13 for connection to a drill stringmember (not shown). A fluid passage 15 directs drilling fluid to anozzle (not shown) that impinges drilling fluid or mud against theborehole bottom to flush cuttings to the surface of the earth.

A pressure-compensating lubrication system 17 is contained within eachsection of the body, there usually being three, which are weldedtogether to form the composite body. The lubrication system ispreferably similar to that shown in commonly assigned U.S. Pat. No.4,727,942, to Galle.

In each section of the body, a lubricant passage 19 extends from eachcompensator 17 downwardly into intersection with another lubricantpassage 21 in which a ball plug 23 is secured to the body by a plug weld25. Lubricant passages 27 carry lubricant to a cylindrical journalbearing surface defined between a cylindrical insert 29 (interferencefit in cutter 33) and a corresponding cylindrical surface on bearingshaft 30, which is cantilevered downwardly and inwardly from an outerand lower region of the body of the bit, commonly known as theshirttail.

Ball plug 23 retains a series of ball bearings 31 that rotatably securecutter 33 to bearing shaft 30. Dispersed in the cutter are a pluralityof rows of earth-disintegrating cutting elements or teeth 35 that may beconstructed of a sintered tungsten carbide secured by interference fitinto mating holes in cutter 33. A seal assembly 37, including asecondary seal according to the present invention, is disposed adjacentthe base of bearing shaft 30 and seals lubricant within the bearing anddebris out of the bearing.

FIGS. 2 and 3 are enlarged section views of the bearing and sealassembly of the earth-boring bit according to the present invention. Apair of axial surfaces 39, 41 formed in cutter 33 and last-machinedsurface 43 of the shirttail portion of the bit body cooperate with apair of radial surfaces 45, 47 to define a bearing seal gland generallyat the base of bearing shaft 30. A single-ring rigid or metal face seal37 is disposed in the seal gland and includes a rigid seal ring 49 andan o-ring energizer 51, which urges a seal face 53 on ring 49 intosealing engagement with a corresponding seal face 41 on an insert 29 incutter 33. This rigid face seal is formed in accordance with commonlyassigned U.S. Pat. No. 4,753,304, to Kelly, which is incorporated hereinby reference.

Seal assembly 37 may be regarded as a primary seal because it isdesigned to seal the journal bearing against entry of foreign materialor debris and to accommodate pressure fluctuations in the lubricant.Seal 37 is also a dynamic seal because it seals the moving or dynamicinterface between each cutter and its bearing shaft and the relativerotational movement between them.

In addition to dynamic seal 37, a secondary seal ring 55 is disposed inthe seal gland opposite between seal assembly 37 and last-machinedsurface 43 to seal the seal gland and seal assembly 37 against entry ofdebris, particularly drilling mud particles, from the exterior of bit11. To accommodate seal ring 55 and seal 37, axial surface 39 is in agroove machined into last-machined surface 43 to a depth approximatelyone-third to one-half the nominal axial thickness of ring 55. However,no groove is believed to be necessary and axial surface 39 may be flushwith last-machined surface 47.

FIG. 4 is an enlarged cross-section view of ring 55 according to thepresent invention. Preferably, secondary seal ring 55 is a continuousring formed of nitrile elastomer material of about 40-45 durometer(Shore A) and a modulus of about 100-200 psi/in/in. According to thepreferred embodiment, no adhesive is used to secure ring 55 in the sealgland. Alternatively, secondary seal ring 55 may be attached or securedby adhesive to axial seal gland surface 39 (or last-machined surface 43)and to rigid seal ring 49 to enhance its sealing ability. Becausesecondary seal ring 55 remains stationary with last-machined surface 47and does not seal relative rotary motion, it is a static seal, asopposed to seal 37, which is a dynamic seal.

According to the preferred embodiment of the present invention, for an81/2 inch bit, secondary seal ring 55 has an outer diameter D ofapproximately 2.480 inch and a radial width W of about 0.211 inch. Outerdiameter D is selected to be about 0.040 to 0.060 inch larger than theouter diameter of rigid ring 49. The inner diameter and end 59 ofsecondary seal ring 55 are configured to be similar to and conform toradial surface 45 and axial surface 39 of the seal gland. A radius R₁ ofabout 0.085 inch and a tip radius R₂ of about 0.015 inch are provided atthe inner end of secondary seal ring 55.

Ring 55 also includes two raised ribs 57 which are approximately 0.025inch to 0.030 inch wide and 0.010 inch to 0.014 inch high. The purposeof the ribs is to form high-stress areas to deter the entry of fluidand/or debris into the seal gland when secondary seal ring 55 is forcedinto contact with surface 39.

Ring 55 has an axial thickness t of about 0.095 inch (in theuncompressed or relaxed state), which is greater than the gap formedbetween axial surface 39 and the end of seal ring 49. The intent is toprovide sufficient "squeeze" on secondary seal ring 55 between axialsurface 39 and seal ring 49. In the preferred embodiment, this squeezeis approximately 20% to 25% of the uncompressed or relaxed radialthickness t of ring 55 using nominal values and with the cutter forcedoutward on the bearing shaft. A radius R₃ of about 0.125 inch isprovided to permit deformation of energizer ring 51 and to closelyconform to it. The remaining width w of ring 55 is about 0.104 inch.

In the assembled configuration, the area in the seal gland bounded bysurfaces 39 and 45, including rings 49, 51, and 55, is intended to beassembled so as to minimize or exclude air. Upon assembly, a continuousring of heavy mineral oil is applied to at least axial surface 39, thensecondary seal ring 55 is placed in the seal gland and energizer 51 andseal ring 49 are installed. This assembly process helps to insure thatvoid areas are minimized and/or eliminated in the aforementioned area ofthe seal gland.

The invention has been described with reference to preferred embodimentsthereof. It is thus not limited, but is susceptible to variation andmodification without departing from the scope of the invention.

We claim:
 1. An earth-boring bit having an improved bearing sealassembly, the earth-boring bit comprising:a bit body; at least onebearing shaft depending inwardly and downwardly from the bit body, thebearing shaft having a base where it joins the bit body; a cuttermounted for rotation on each bearing shaft, the cutter including axialand radial surfaces that cooperate with the base of the bearing shaft todefine a bearing seal gland, the axial surface of the cutter being in aplane substantially perpendicular to an axis of the bearing shaft, theradial surface being an annular surface concentric with the axis; adynamic primary seal element disposed in the seal gland, the primaryseal element having a rigid seal ring that is in dynamic contact withthe axial surface of the cutter and a resilient energizer disposed inthe seal gland in contact with the rigid seal ring and the bearing shaftfor urging the rigid seal ring against the axial surface of the cutter;and a static secondary seal element formed of resilient material anddisposed in the seal gland at the base of the bearing shaft, thesecondary and primary seal elements being free of relative motiontherebetween and being free of contact with the radial surface of thecutter, and wherein the secondary seal element and the primary sealelement cooperate to seal the gland against entry of matter and protectthe energizer of the primary seal element from debris.
 2. Theearth-boring bit according to claim 1 wherein the secondary seal elementcontacts and seals against at least the rigid seal ring of the primaryseal element.
 3. The earth-boring bit according to claim 1 wherein thesecondary seal element is a continuous elastomeric ring secured to thebit body at the base of the bearing shaft.
 4. The earth-boring bitaccording to claim 1 wherein the bit body includes a last-machinedsurface adjacent the base of the bearing shaft and the secondary sealelement is located adjacent to the last-machined surface.
 5. Theearth-boring bit according to claim 4 wherein a mineral oil is disposedbetween the last-machined surface and the secondary seal element forfilling void space in the seal gland.
 6. The earth-boring bit accordingto claim 1 wherein the secondary seal element is elastomeric, sealsbetween the base of the bearing shaft and a portion of the rigid sealring, and is in contact with a portion of the energizer.
 7. Theearth-boring bit according to claim 1 wherein the secondary seal elementis a resilient ring secured to a portion of the primary seal element. 8.An earth-boring bit having an improved bearing seal assembly, theearth-boring bit comprising:a bit body; at least one bearing shaftdepending inwardly and downwardly from the bit body, the bearing shafthaving a base where it joins the bit body; a cutter mounted for rotationon each bearing shaft, the cutter including axial and radial sealsurfaces that cooperate with the base of the bearing shaft to define abearing seal gland, the axis surface of the cutter being in a planesubstantially perpendicular to an axis of the bearing shaft, the radialsurface being an annular surface concentric with the axis; a primaryseal element disposed in the seal gland, the primary seal elementincluding a rigid seal member and a resilient member for urging therigid seal member into sealing contact with a sealing surface; and aresilient, elastomeric, secondary seal element disposed in the sealgland between the base of the bearing shaft and the primary seal,wherein the secondary seal element and the primary seal elementcooperate to jointly protect the resilient member from debris and sealthe seal gland against entry of debris.
 9. The earth-boring bitaccording to claim 8 wherein the primary seal element and the secondaryseal element are free of contact with the radial seal surface of thecutter.
 10. The earth-boring bit according to claim 8 wherein thesecondary seal element contacts and seals against both the rigid sealmember and the resilient member of the primary seal element.
 11. Theearth-boring bit according to claim 8 wherein the secondary seal elementis a continuous elastomeric ring secured to the bit body at the base ofthe bearing shaft.
 12. The earth-boring bit according to claim 8 whereinthe bit body includes a last-machined surface adjacent the base of thebearing shaft and the secondary seal element is located adjacent to thelast-machined surface.
 13. The earth-boring bit according to claim 12,wherein a mineral oil is disposed between the last-machined surface andthe secondary seal element for filling void space in the seal gland. 14.The earth-boring bit according to claim 8 wherein the secondary sealelement comprises at least one elastomeric material.
 15. Theearth-boring bit according to claim 8 wherein the secondary seal elementis a resilient ring secured to the rigid seal member of the primary sealelement.
 16. An earth-boring bit having an improved bearing sealassembly, the earth-boring bit comprising:a bit body; at least onebearing shaft depending inwardly and downwardly from the bit body, thebearing shaft having a base and a last-machined surface where it joinsthe bit body; a cutter mounted for rotation on each bearing shaft, thecutter including radial and axial seal surfaces that cooperate with thebase of the bearing shaft to define a bearing seal gland, the axialsurface of the cutter being in a plane substantially perpendicular to anaxis of the bearing shaft, the radial surface being an annular surfaceconcentric with the axis; a primary seal element disposed in the sealgland, the primary seal element including at least one rigid seal ringand at least one resilient energizer element between the bearing shaftand the rigid seal ring for urging the seal ring into sealing engagementwith the axial seal surface of the cutter; a resilient, elastomericsecondary seal element disposed in the seal gland opposite the axialseal surface of the cutter in stationary contact with the last machinedsurface, the secondary seal element contacting and sealing against boththe rigid seal ring and the energizer element of the primary sealelement, and wherein the secondary seal element and the primary sealelement cooperate to protect the energizer element from debris and sealthe gland against entry of debris; and wherein the primary and secondaryseal elements are free of contact with the radial seal surface of thecutter.
 17. The earth-boring bit according to claim 16 wherein thesecondary seal element is a continuous ring secured to the bit body atthe base of the bearing shaft.
 18. The earth-boring bit according toclaim 16 wherein the secondary seal element is secured to thelast-machined surface;wherein the secondary seal element is a resilientring secured to a portion of the primary seal element.
 19. Theearth-boring bit according to claim 18 wherein a mineral oil is disposedbetween the last-machined surface and the secondary seal element forfilling void space in the seal gland.
 20. The earth-boring bit accordingto claim 16 wherein the secondary seal element is an resilient ringsecured to the rigid seal ring of the primary seal element.